The invention relates to dispensing a predetermined quantity of a multi-component composition in which the components undergo an undesirable chemical reaction with each other when brought into contact with each other.
Dental primer-adhesive compositions are applied to a tooth prior to addition of a material such as a dental restorative or composite in order to enhance adhesion between the tooth and the restorative or composite. Examples of useful primer-adhesive composition, described in Aasen et al., U.S. Pat. No. 4,719,149 and Aasen et al., U.S. Pat. No. 5,525,648, hereby incorporated by reference, feature water, an acid, and one or more polymerizable, film-forming components (i.e., components that form a film upon polymerization); an actinic radiation-sensitive curative and a non-polymerizable polymer may be included as well. The purpose of the acid is to etch the tooth surface. The film-forming component, upon polymerization, forms a film on the etched tooth surface to enhance adhesion between the tooth and a subsequently applied restorative or composite. A particularly useful primer-adhesive composition includes water, maleic acid, hydroxy ethyl methacrylate ("HEMA"), a polyalkenoic acid having polymerizable groups (e.g., acrylate or methacrylate groups), and curative.